Modern wireless communications standards require radio frequency (RF) communications circuitry to be capable of transmitting and receiving wireless signals over a wide frequency range. A fixed antenna can generally only transmit and receive signals efficiently within a relatively narrow frequency range. Accordingly, tunable antennas, antenna tuning circuitry, antenna impedance matching circuitry, and feedback mechanisms are often used to increase the frequency range over which an antenna can efficiently transmit and receive signals. FIG. 1 shows conventional antenna aperture tuning circuitry 10. For context, a radiating antenna element 12 and an antenna feed point 14 are also shown. The conventional antenna aperture tuning circuitry 10 includes a number of resonators 16 coupled between the radiating antenna element 12 and ground. Each one of the resonators 16 includes a resonator inductor L_R and a resonator capacitor C_R. The resonant frequency of each one of the resonators 16 determines the resonant response of the radiating antenna element 12, which affects the transmission and reception quality thereof at different frequencies. Signals received at the radiating antenna element 12 are provided to the antenna feed point 14, which is used to connect the radiating antenna element 12 to additional circuitry. Similarly, signals from the antenna feed point 14 are radiated from the radiating antenna element 12 for transmission.
While the conventional antenna aperture tuning circuitry 10 is capable of tuning the radiating antenna element 12 for a number of different frequencies, the bandwidth of the conventional antenna aperture tuning circuitry 10 is limited. That is, while the conventional antenna aperture tuning circuitry 10 may be capable of tuning a response of the radiating antenna element 12, the width of the pass-band (i.e., the bandwidth) thereof is generally directly proportional to the number of resonators used. Conventional antenna aperture tuning circuitry 10 may require a separate resonator for each operating band that is supported. This may in turn require a large number of inductors and capacitors, which consume a large amount of space in a mobile device and increase the cost thereof, and complex control circuitry for switching in and out these inductors and capacitors.
Antenna impedance matching circuitry is generally used along with antenna aperture tuning circuitry in order to further increase the performance of an RF communications device. In particular, antenna impedance matching circuitry is provided between an antenna and downstream circuitry such as RF front end circuitry in order to match an impedance between the antenna and the downstream circuitry. There are many well-known antenna impedance matching circuit topologies, most or all of which suffer from the same problems above of relatively narrow bandwidth and marginal performance.
FIG. 2 thus shows conventional RF front end circuitry 18 including antenna impedance tuning circuitry. The conventional RF front end circuitry 18 includes an antenna 20, RF multiplexer circuitry 22, and antenna impedance tuning circuitry 24 coupled between the antenna 20 and the RF multiplexer circuitry 22. The antenna impedance tuning circuitry 24 includes a number of resonators 25 coupled between the signal path between the antenna 20 and the multiplexer circuitry 22 and ground. Each one of the resonators 25 includes a resonator inductor L_R and a resonator capacitor C_R coupled in parallel. The resonant frequency of each resonator is relatively narrow, and therefore a bandwidth of the antenna impedance tuning circuitry 24 is limited. While additional resonators may be added to increase the bandwidth of the antenna impedance tuning circuitry 24, doing so comes at the cost of increased space, cost, and complexity.
In a further effort to meet the stringent requirements of many modern wireless communications standards, feedback mechanisms have widely been implemented in order to dynamically adjust signals provided from a wireless communications device. FIG. 3 thus shows conventional power coupler circuitry 26, which may be used to implement one or more such feedback mechanisms. For context, an antenna 27, a transmission line 28, and the RF multiplexer circuitry 22 coupled to the antenna 27 via the transmission line 28 are also shown. The power coupler circuitry 26 includes a power coupler 30 and a termination impedance Z_T. The power coupler 30 includes an isolated node 32, a coupled node 34, and a coupling line 36 between the isolated node 32 and the coupled node 34. The termination impedance Z_T is coupled between the isolated node 32 and ground.
In operation, a portion of electromagnetic power on the transmission line 28 is coupled into the coupling line 36 of the power coupler 30. The amount and type of electromagnetic power coupled from the transmission line 28 to the coupling line 36 is determined by the termination impedance Z_T. The signals on the coupling line 36 are provided to the coupled node 34, where they may be used to dynamically adjust one or more parameters of the RF front end circuitry 18.
FIG. 4 shows the power coupler circuitry 26 wherein the termination impedance Z_T is replaced by an LC resonator 38. The LC resonator 38 includes a resonator inductor L_R and a resonator capacitor C_R coupled in parallel between the isolated node 32 and ground. The resonant frequency of the LC resonator 38 determines a response of the power coupler circuitry 26 on the transmission line 28. In particular, at the resonant frequency of the LC resonator 38, the impedance presented at the isolated node 32 is essentially an open circuit, while at all other frequencies the impedance presented at the isolated node 32 is significantly reduced. This provides good coupling at one frequency, but relatively poor coupling at all other frequencies.
FIG. 5 shows the power coupler circuitry 26 including an additional power coupler 40 and an additional LC resonator 42. The additional power coupler 40 and the additional LC resonator 42 are identical to those described in FIG. 2, such that the additional power coupler 40 includes an isolated node 44, a coupled node 46, and a coupling line 48 between the isolated node 44 and the coupled node 46. The additional LC resonator 42 includes a resonator inductor L_R and a resonator capacitor C_R coupled in parallel between the isolated node 44 and ground. In operation, the LC resonator 38 is tuned to resonate at a first frequency, while the additional LC resonator 42 is tuned to resonate at a second and different frequency. The different resonant frequencies of the LC resonator 38 and the additional LC resonator 42 combine to effectively double the bandwidth of the antenna (either contiguously or non-contiguously). Accordingly, the power coupler circuitry 26 may be used to sense signals within a wider frequency range. However, using the additional LC resonator 42 comes at the cost of significantly increased area, cost, and complexity of the RF front end circuitry 18.
In light of the above, there is a need for antenna aperture tuning circuitry, antenna impedance matching circuitry, and power coupler circuitry with improved performance. In particular, there is a need for antenna aperture tuning circuitry and antenna impedance matching circuitry configured to increase the usable bandwidth of an antenna with reduced complexity and distortion. Additionally, there is a need for compact power coupler circuitry that is usable over a large bandwidth.